This invention relates generally to electrostatic latent image development systems that develop images with use of marking particles provided in a developing material, and, more particularly, relates to systems for electrostatic development of a latent image, wherein marking particles are cleaned from a supporting surface.
Various methods of toner cleaning have been described in the art of electrostatographic printing and copying systems. A typical electrostatographic printing process includes a development step whereby a quantity of developing material is physically transported into the vicinity of an imaging member bearing a latent image. Marking materials (known as marking particles, toner particles, or toner) in the developing material are caused to migrate via, e.g., electrical attraction, to the image areas of the latent image so as to selectively adhere to the imaging member in an image-wise configuration, so as to provide a developed image. The developed image is typically transferred to a copy substrate. The residual toner, typically present in a background image, is usually removed in preparation for a subsequent imaging cycle. A simple blade cleaning apparatus may be employed; other cleaning devices may include a brush or roller member for removing toner from the surface on which it resides. The removed toner may be transported to a toner sump or other conservation vessel so that the waste toner can be reclaimed for subsequent use.
In accordance with one aspect of the present invention, there is provided a toner cleaning system for cleaning toner from a supporting surface. A movable member includes a carrier permeable segment featuring a porous structure. The movable member is employed to engage the supporting surface so as to receive therefrom the toner layer. The microporous structure includes pores slightly smaller than the particle size of the toner particles in the toner layer such that the toner layer may be temporarily supported on the movable member until removal therefrom is desired. A quantity of carrier fluid is provided at an inner surface of the carrier permeable segment. The porous structure allows carrier fluid to flow therethrough in response to an applied carrier fluid transport force so as to reduce or eliminate the bond between the toner layer and the exterior of the carrier permeable segment, thus forcing the toner layer to at least partially disengage from the exterior surface of the carrier permeable segment. The disengaged portion of the toner layer than falls away from the exterior surface of the carrier permeable segment, or is easily collected therefrom by suitable collection means. The toner and any carrier fluid thus removed from the carrier permeable segment may be collected and conserved for reuse, if desired.
Of particular interest with respect to the present invention is the electrostatographic printing process known as contact electrostatic printing, wherein a thin layer of liquid developing material is formed on a first surface of a first member, wherein the layer has a high concentration of charged toner, and is subjected to an electrostatic latent image. Development of the latent image than occurs wherein toner particle migration or electrophoresis is replaced by direct surface-to-surface transfer of a toner layer induced by image-wise fields. For the purposes of the present description, the concept of latent image development via direct surface-to-surface transfer of a toner layer via image-wise fields will be identified generally as contact electrostatic printing (CEP). Exemplary patents which may describe certain general aspects of contact electrostatic printing, as well as specific apparatus therefor, may be found in U.S. Pat. Nos. 4,504,138; 5,436,706; 5,596,396; 5,610,694; and 5,619,313.
Accordingly, and in another aspect of the present invention, there is provided an imaging system for effecting contact electrostatic printing of an image, wherein the imaging system includes at least one contact electrostatic printing engine operable upon a copy substrate. A toner cleaning system is operable in the printing engine. The printing engine includes a transport which moves a latent image bearing member along a path. A toner layer is brought into pressure contact with the latent image bearing surface of the latent image bearing member such that a developed image is created by separating and selectively transferring, portions of the toner layer in correspondence with the image and non-image regions of the latent image. A toner cleaning system is disposed adjacent to the latent image bearing surface. The toner cleaning system includes a movable member having a carrier permeable segment. The movable member is employed to engage the supporting surface so as to receive therefrom the toner layer, thereby cleaning the residual toner layer from the latent image bearing surface. Carrier fluid flow through the carrier permeable segment in response to an applied carrier fluid transport force reduces or eliminates the bond between the toner layer and the exterior of the carrier permeable segment, thus forcing the toner layer to at least partially disengage from the exterior surface of the carrier permeable segment.
In accordance with another aspect of the present invention, a toner cake delivery and cleaning apparatus may be constructed and operated in first and second modes, each of which are useful in the operation of the contact electrostatic printing process to which the present invention is directed. In a first mode of operation, for effecting toner cake delivery, a toner cake layer of high solids content is created on a carrier permeable segment of a coating member. To do so, a low solids content liquid developing material applicator provides a relatively uniform layer of low solids content liquid developing material onto the carrier permeable segment. The layer of low solids content liquid developing material is subject to a rapid adsorption of at least a portion of the carrier fluid away from the layer of liquid developing material. As a result, a reduction of the ratio of carrier fluid to toner solids in the liquid developing material layer results in the formation of the desired toner cake layer. The toner cake layer is then available for transfer to the surface of a receiving member for subsequent use in development of an electrostatic latent image. For example, the toner cake layer may undergo pressure contact with the surface of an imaging member which bears a latent image. A developed image is subsequently created by separating and selectively transferring portions of the toner cake layer to an image separator in correspondence with the image and non-image regions of the latent image. The developed image and non-image areas are separated at the exit of the process nip. Further rotation of the image separator allows the developed image to be transferred from the surface of the image separator to a copy substrate carried on a substrate transfer path.
In the second mode of operation, rotation, of the imaging member allows a toner layer, such as the portions of residual toner cake from the non-image areas, to be transferred to the carrier permeable segment. The carrier permeable segment is then subjected to a flow of carrier fluid to cause the toner layer to be detached from the carrier permeable segment for subsequent collection by toner collection means.